There have been proposed lithium secondary batteries in which the positive electrode or the negative electrode is highly insulated by using a protective tape.
Patent Literature 1 discloses a lithium secondary battery in which breakage of the current collector at a part where the current collector is in contact with the lead is suppressed.
FIG. 4 illustrates the structure of the positive electrode of the lithium secondary battery disclosed in Patent Literature 1, where FIG. 4(A) is a partial top view observed from one main surface side of the current collector, and FIG. 4(B) is a sectional view taken along line L1-L1 in FIG. 4(A). In FIG. 4, the reference character 21A indicates a current collector and the reference character 21B indicates an active layer.
In a double-sided uncoated part 21b, a protective layer 28 having a rectangular plane outer shape is famed on a positive electrode current collector-exposed surface 21a. The protective layer 28 is formed approximately in the middle of the double-sided uncoated part 21b. Part of the middle portion of the protective layer 28 is interposed between the lower end portion of the lead 25 and the positive electrode current collector-exposed surface 21a such that part of the protective layer 28 is surrounded by the lower edge of the lead 25, part of the two-side edges of the lead 25, and the positive electrode current collector-exposed surface 21a. Examples of the protective layer 28 include a resin layer, an inorganic material layer, and the like. Examples of the resin layer include a resin film and a resin tape. Examples of the resin film include a resin coating film containing a resin, such as a PVDF (polyvinylidene fluoride) film. Examples of the resin tape include a PP (polypropylene) tape, a PI (polyimide) tape, and a PET (polyethylene terephthalate) tape. Examples of the inorganic material layer and the like include an inorganic tape. The protective tape 27 covers the positive electrode current collector-exposed surface 21a, the lead 25, and the protective layer 28 on one main surface side of the positive electrode current collector 21A and covers the positive electrode current collector-exposed surface 21a on the other main surface side of the positive electrode current collector 21A. The protective tape 27 is intended to, for example, prevent heat generation of the battery if the positive electrode 21 comes into contact with the negative electrode 22 because of a fracture of the separator or the like under abnormal battery conditions. The protective tape 27 is, for example, a resin tape.
As an example for using a tape at a different position, Patent Literature 2 discloses that an insulating tape is famed of a composite material tape, and the composite material tape includes an organic material forming a base layer and an inorganic material dispersed in the organic material. The inorganic material content is 20% to 80% of the total weight of the composite material tape.